Nerve allografts (grafts between genetically different members of the same species) are rejected by normal rats but not by rats that have been treated with the immunosuppressive agent cyclosporin A (CyA). Further studies have shown that host axons can regenerate through allografts in CyA-treated hosts and that these axons will reinnervate denervated muscles. CyA also prevents the rejection of nerve allografts in allogeneically sensitized recipients, but the drug is ineffective in preserving xenografts (grafts between different species; e.g., guinea pig and rat). Immunosuppressive treatment with CyA had to be continuous because if therapy is stopped, rejection occurs even when only minor histoincompatibilities exist. Allogeneic muscle and neurons also survive during CyA treatment; in the case of muscle, it becomes reinnervated by host axons while transplanted neurons can regenerate their axons and induce taste buds in tongue tissue.